1. Field of the Invention
The present invention relates to an aqueous coating composition.
2. Discussion of Background
Heretofore, it has been known that copolymers made of a fluoroolefin, a cyclohexyl vinyl ether and various other monomers, are soluble in organic solvents at room temperature, and when used as coating materials, they provide transparent coating layers having high gloss and excellent properties of fluorinated resins, such as high weather resistance, water and oil repellency, stain resistance and non-adhesiveness (e.g. Japanese Unexamined Patent Publication No. 44083/1980). Their use is increasing in the field of e.g. building construction.
However, such copolymers are hardly applicable to a coated substrate having a low solvent-resistance which is apt to be corroded by the above organic solvents. For example, when the coating material is applied to an old aged, deteriorated coating layer for repairment, the deteriorated coating layer may sometimes happen to peel off partly.
On the other hand, in recent years, there have been restrictions against use of organic solvents from the viewpoint of air pollution. Further, organic solvents volatilized during the coating step at factories or sites for coating may substantially adversely affect human bodies. Particularly, solvents such as esters or ketones tend to cause, for example, paralysis or swelling in respiratory organs or nerves, and further sometimes cause symptom of poisoning. Under these circumstances, the demand is increasing for aqueous coating materials or powder coating materials which employ no organic solvents. Such studies have been made also with respect to fluorine resins, and it has been reported that fluorine resins having no functional groups can be prepared by emulsion polymerization (Japanese Unexamined Patent Publication No. 25411/1980).
Further, fluorine-containing copolymers having functional groups such as hydroxyl groups obtained by emulsion polymerization have been disclosed in Japanese Unexamined Patent Publications No. 34107/1982 and No. 31044/1986. Furthermore, aqueous dispersions of fluorine-containing copolymers having the mechanical stability and chemical stability improved, have been proposed in, for example, Japanese Unexamined Patent Publication No. 207352/1988.